import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class UdpEchoServer {
    private DatagramSocket socket=null;

    public UdpEchoServer(int port) throws SocketException {
        socket=new DatagramSocket(port);//手动指定端口
    }
    public void start()throws IOException {
        System.out.println("服务端启动！");
        while (true){
            //1读取请求并解析
            DatagramPacket requestPacket=new DatagramPacket(new byte[4096],4096);
            socket.receive(requestPacket);
            //recieve之后，数据以二进制存储到DatagramPacket中，要想显示出来必须转化为字符串
            String request=new String(requestPacket.getData(),0,requestPacket.getLength());
            //此处为计算响应，然后写回客户端
            String response=process(request);
            //搞一个响应对象，把数据构造进去,再通过send送出去
            DatagramPacket responsePacket=new DatagramPacket(response.getBytes(),response.getBytes().length,requestPacket.getSocketAddress());
            socket.send(responsePacket);
            //打印一个日志，把交互的数据情况显示出来
            System.out.printf("[%s:%d] req=%s, resp=%s\n",requestPacket.getAddress().toString(),requestPacket.getPort(),request,response);
        }
    }

    public String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer server=new UdpEchoServer(9090);
        server.start();
    }
}
